If you’re using a cartridge razor today, you know that the real cost is not in the razor, but in buying the replacements cartridges. In the same way, and for the same reasons, the real cost of using a DE back in the day was the replacement blades. This created the market for razor blade sharpeners as well as self sharpening razors (the Shake Sharp razors springs to mind). The cost also inspired Bertil Åström of Sweden to invent a simple and non-expensive safety razor;

The chief object of this invention is to create a simple and non-expensive safety razor uniting the advantages of the ordinary or knife razor and those of the so-called safety razors, while eliminating the disadvantages of the known razors.

In other words, combining the advantage of the straight’s everlasting blade with the shaving simplicity of a hoe type safety razor… while at the same time making the razor simple to manufacture, use, and maintain – without a top cap.

Another object of this invention is to render it possible to remove or to insert the blade in one single operation, i. e. in one single manipulative step […] while the non-cutting parts remain as a single, assembled aggregate
A further object of this invention is to construct the safety razor in such blade is always automatically exactly centred and kept in its correct position.
A further object of this invention is to construct manner that the a safety razor without any clamping plate on the blade, so that the razor has only a comb-shaped safety plate or guard below the blade.

So that is four things to achieve all at once, and the way Mr Åström went about achieving them is both simple and easy to manufacture. The patent drawing does a pretty good way of explaining it.

The whole razor consists of three major parts: A blade of a unique shape with a cut out in the back, a bolt and the handle with attached base plate…. and that’s it
The countersunk keyhole in the back of the blade makes for easy assembly and disassembly – the cone shaped head of the bolt easily and repeatedly locates and lock the blade in the correct spot – while the shape of the blade itself do away with the need for a top cap. That is two of the for items taken care of.
According to the patent the thickness of the blade increases the rigidity and reduces blade vibration, which should lead to the edge lasting much longer than the ordinary thin safety razor blades. Mr Åström also claimed that the angle of the edge would result in a  very efficient and painless shave.
The keyhole slot also means that one don’t have to to unscrew the bolt more than a few threads, leaning it secured to the rest of the razor, while the base plate (referred to as a carrier plate) is permanently fastened to the handle proper. That takes care of the two last items on the list.
To disassemble the razor, all the user have to do is to loosen the nut on the end of the handle and the blade will be free to slide off the carrier plate. To assemble it again after cleaning and/or honing the blade, all the user have to do is to slip the blade in place under the bolt head and tighten the nut. All told as easy as a twist to open DE, and with less parts to keep track of than a three piece safety razor.
The shape of the blade itself is another stroke of genius, and one that isn’t explicitly mentioned in the patent text; unlike a straight razor – or the blades used in most wedge-razors – it only needs to be honed on one side. Setting up the edge of a razor blade (or a knife, for that matter) takes a fair bit of skill, but Mr Åström made it a lot simpler with the shape of this blade.
Overall I’m quite impressed with the well though out simplicity of the design. As far as I can see it achieves it’s four stated goals, while additionally providing a blade design that would be far easier to maintain than the two sided hollow ground of most straight razors and wedge razors. It is a shame that the design don’t seem to have gone beyond the patent (which have expired by now, in case someone has a machine shop…).

Want to eek out a little more life from your double edged blade? Recoup a little bit more on the investment as it were? To us today that don’t make much sense, since we’re just paying pennies per blade, but back in the day blades were more costly; about equivalent to the cost of a razor cartridge today per blade!

Much like you today can find sharpeners for cartridge razor, there was a market for DE-sharpeners back in the day. One of the earliest that I found a patent for was granted in March 1911, and was submitted by Eleazer I Rains. As far as I can tell it is Mr Rains’ only shaving related patent.

The machine he patented is simple enough in principle, but the actual execution might leave a little something to desire… it’s not a handle little device you can keep in a drawer, it’s a fairly big lump of machinery you bolt to your bathroom counter.

The device consists of two geared sharpening rollers (which could be made adjustable) against which a blade could be pressed by a spring… and that is about it when you come down to it. This is a principle which several other sharpeners adopted later, in various forms.

In Mr Rains’ own words, the machine is

comprising a sharpening roll, `means to rotate the same, a spring pressed blade support adapted to press the blade yieldingly toward the roll, and movable “bodily toward and from the roll, and guides in which said support is loosely guided

I don’t know if this sharpener was ever built, manufactured or sold, but as far as I can tell from the drawings it should work as intended. The major failing I can see with the design of it is the sheer bulk and the need to bolt it to a countertop.

Very often a patent description starts out with a claim stating something along the line of “…have invented a new and improved…” or “…certain improvements to…”. The patent we’re looking at today on the other hand do NOT start with such a claim, and it is quite telling.

Instead George R Harvey – when he filed his claim in April of 1932 – simply starts with a very short description of what it’s all about: “Combination razor and shaving brush in advance of the razor.”

Wait.. what? In advance of? What do that even?

Well… the logic isn’t too far of the so called “lube strips” on certain modern cartridge razors, even if Mr Harvey’s design probably did more for lubrication and skincare.

The key to the invention, as far as I can tell, is that the single edge razor have a hollow handle you can fill with shaving cream. The bottom of the handle is a plunger, much like a syringe, which forces the cream out through a nozzle onto which there is mounted a short brush. The drawing makes it easy to understand:

How would this rather clumsy looking device be to use? In Mr Harvey’s own words:

In the operation of the device the compartment 3 being charged with a soap or other emollient, the brush 9 is first dampened and the plunger 14 is then rotated so as to-cause the desired amount of the material to be discharged through the slots 13 onto the tufts of the brush. The instrument is then drawn over the face of the user so as to cause the brush to travel in advance of the cutting edge of the blade, the brush applying the material to the face and the razor then performing its function in a manner which will be readily understood.

I strongly suspect that Mr Harvey had a mustache…  there is no way this contraption would both lather and shave the upper lip without both cutting your nose while lathering and getting a taste of shaving cream while shaving.